Technical Field
The present invention relates to an acidic drilling fluid system, wherein the system comprises an aqueous acidic solution, a silicate, and a hydro-carbon based isolation fluid, and wherein the system targets a hydrocarbon producing formation with zero invasion. The invention further includes a method of forming a zero-invasion seal on the face of a well bore using the acidic drilling fluid system.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
The design of drilling fluid typically includes several additives that are compatible with reservoir fluids and a spectrum of accurately sized solids that can prevent filtration but still provide a thin cake. It is a common practice to enhance the properties of the drilling fluid to control the stability of oil and gas wells as well as to handle its regular function of the drilling fluid. Several ways exist to select drilling fluid additives and their design depends on the way the drilling fluids are executed or the fluid used therein. When these fluids are pumped at pressures higher than the formation pore pressure, the operation is referred to as an overbalance drilling operations. In overbalance drilling operations, one of the drilling fluid's basic functions is to exert hydrostatic pressure over the permeable formation to prevent kicks since the drilling fluid pressure is normally kept above the formation pore pressure. The positive pressure differential between the drilling fluid and formation pore pressure causes the drilling fluid to invade the permeable formation hence the suspended solids in the mud are deposited on the face of the permeable formation to build a filter cake over the formation face, decreasing the rate of filtrate invasion. In addition to the deposition of drilling mud particles on the formation face around the wellbore, the small particles in the mud invade the formation causing damage surrounding the wellbore. Normally, the depth of particles invasion depends on the filter cake permeability, drilling fluid design, and pore size.
Filter cake or mud cake is used conventionally during drilling operations to prevent fluid losses to the formation and to allow good circulation of drilling fluids and suspended cuttings to the surface for removal from the well. Formation of an effective filter cake depends on a very well designed drilling system including mud fluids and additives. The drilling fluid is normally designed for minimum infiltration and solid invasion into the formation. On one hand, the filter cake must withstand high differential overbalance pressures. On the other hand, reduced oil and gas production can result from reservoir damage when a poor filter cake allows deep filtrate invasion. The drilling mud systems undergo comprehensive testing procedures to determine infiltration rate and filter cake properties such as thickness, toughness, slickness and permeability.
Typically, the cuttings formed as a drill removes portions of a formation separate from the drilling mud and are removed using contaminant removal equipment. The effect of introducing formation cutting particles, if not separated, to the drilling fluid during the drilling operation is significant from the point of view of the filter cake's properties. The presence of particles will degrade the performance of the drilling fluid as well as increase the filter cake thickness and permeability. Therefore, forming an effective thin impermeable filter cake still one on the most hard and a challenging tasks of drilling operations.
For long horizontal well sections the filter cake's properties are not constant, heterogeneity effects are often more severe in horizontal wells than in vertical wells because of axial variation of the depth of the damage surrounding the wellbore. This is also significant difficulty that must be overcome in order to improve drilling operations. Although several methods may be employed to overcome this challenge, e.g., use of a smart drilling fluid, there is no existing technique that enables pumping the drilling fluids with good diversion of the fluids. Generally, when a long horizontal formation is drilled, the drilling fluids tend to get deeper invasion in more highly permeable parts of the well. Therefore, the zone with high permeability receives heavy fluid and particle invasion whereas the parts with low permeability receive less damage. On the other hand, in homogeneous formations, especially for long laterals, fluid tends to invade deeper in the heel of the well due to the long time the heel is exposed to drilling. Less invasion occurs in parts of the well away from the heel, e.g., the “toe”.
A method and drilling fluid system that can be used to generate quick, thin, uniform and impermeable filter cake layer in horizontal and vertical wells has so far not been available. Moreover, there is a need for improved drilling system compositions and methods of using drilling fluid system that result in zero invasion into a well formation, do not damage the formation, and form a sealing layer only on the face of the formation.